Field of the Invention
The present invention relates to an object information acquiring apparatus and a processing method.
Description of the Related Art
As a technique to acquire information on the interior an object, such as a living body, by receiving an acoustic wave, a photoacoustic imaging apparatus, an ultrasonic echo imaging apparatus or the like has been proposed. The photoacoustic imaging apparatus is particularly effective in diagnosing skin cancer and breast cancer, and is expected to replace the ultrasonic echo diagnosis apparatuses, X-ray apparatuses, MRI apparatuses and the like which have been conventionally used.
A photoacoustic imaging apparatus makes information on an object (e.g. living body) visible, utilizing the photoacoustic effect. The photoacoustic effect is a phenomenon where a light absorbing substance (e.g. hemoglobin in blood) inside the object, which is irradiated with visible light, a near infrared or the like, is momentarily expanded by the absorbed light energy, and generates a photoacoustic wave. A tomography technology using this photoacoustic effect is called “photoacoustic tomography”.
In photoacoustic imaging, information related to the absorption coefficient inside the object can be imaged. The absorption coefficient is a light energy absorption rate of the tissue of the living body. An example of information related to the absorption coefficient is initial sound pressure, which is sound pressure at the moment when the photoacoustic wave is generated. The initial sound pressure is in proportion to the product of the light energy (light intensity) and the absorption coefficient, hence the absorption coefficient can be calculated based on the initial sound pressure value. Furthermore, the absorption coefficient depends on the concentration of the constituents of the tissue of the living body, hence the concentration of the constituents can be acquired from the absorption coefficient. In particular, the concentration ratio between oxyhemoglobin and deoxyhemoglobin, and the oxygen saturation of the tissue of the living body can be acquired by using the light having a wavelength that can easily be absorbed by hemoglobin in blood. By analyzing the oxygen saturation distribution, tumorous tissue inside the living body and peripheral tissue of the tumor and the like can be identified, therefore photoacoustic imaging is expected to be applied to medical diagnosis.
Minghua Xu and Lihong V. Wang, “Universal back-projection algorithm for photoacoustic computed tomography”, PHYSICAL REVIEW E 71, 016706 (2005) discloses a universal back projection (UBP), which is one back projection method, as a method of imaging initial sound pressure from a receiving signal acquired by a transducer, which receives an ultrasonic wave and converts it into an electric signal.
Non Patent Literature 1: Minghua Xu and Lihong V. Wang, “Universal back-projection algorithm for photoacoustic computed tomography”, PHYSICAL REVIEW E 71, 016706 (2005)